This invention relates to devices for measuring small pressure differences in fluids. More specifically, this invention relates to the measurement of small pressure differences in fluids which are in the range of about 0.1 to 1,000 dynes/square centimeter.
Numerous methods have been devised to measure fluid pressure differences. These methods include measuring relative height differences in a fluid as, for example, in a manometer-like device. A "manometer-like device" means throughout this specification and the claims a relative pressure measuring device wherein a first pressure is measured relative to a second pressure by balancing the difference in pressure between said first and said second pressure by a fluid head. A "fluid head" means throughout this specification and claims the product of the difference in relative heights between a first fluid level, e.g., a first liquid, and a second fluid level, e.g., a second liquid, times the density of said first and second fluid, when said first and second fluid are of the same density. More generally, a fluid head, where two immiscible fluids, e.g., liquids, make up the "fluid head" requires a balancing of the contributions made by each of the fluids, as would be clear to one of skill in the art. Two deficiencies associated with these manometer-like devices are that the measurement of small pressure differences is neither continuous nor easily adaptable to recording devices, such as millivolt recorders.
A pitot tube is a known device for measuring the rate of fluid movement. However, since the pressure differences in a pitot tube due to movement of a fluid can be very small, the usefulness of such a device is limited. For example, air at room temperature (72.degree. F.) moving at a rate of about 0.46 ft/second gives rise to a water pressure differential of about one micron.